1. Field of the Invention
The present invention relates to an apparatus for inspecting a display panel of a flat panel display device, and more particularly, to a visual inspector for inspecting a flat panel display device.
2. Discussion of the Related Art
Flat panel display devices are designed to be smaller in volume and lighter in weight than cathode ray tube display devices. Flat panel display devices include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and light emitting diode (LED) displays.
An apparatus of the related art is used to examine flat panel display devices to determine their quality. A light is projected onto the display panel (for example, an LCD panel) using the apparatus and a worker examines light reflected from the display panel to detect and evaluate defects in the display panel that will result in a low quality display during operation.
A visual inspector is an apparatus for performing a naked eye inspection of a display panel.
The visual inspector is designed to allow evaluating differences in light reflection at different illumination angles to determine whether the display panel is of inferior quality.
In a visual inspection process according to the related art, reflective illumination and transparent illumination are used to perform a reflective illumination inspection and a transparent illumination inspection, respectively.
The visual inspector of the related art includes an illumination structure (hereinafter referred to as a “reflective illumination unit”) for providing reflective illumination and another illumination structure (hereinafter referred to a “transparent illumination unit”) for providing transparent illumination, respectively.
In a visual inspection method of the related art, the transparent illumination unit is positioned at a predetermined distance (inspection distance) from a place where the inspection is carried out (hereinafter referred to as an “inspection unit”) during the transparent illumination inspection.
During the reflective illumination inspection of the related art, the display panel is inclined at an angle to the vertical direction. Accordingly, the transparent illumination unit may interfere with the inclined display panel if the transparent illumination unit is positioned near the inspection unit. To prevent this interference, the transparent illumination unit is moved away form the inspection unit by a predetermined distance when carrying out the reflective illumination inspection. The time during the movement of the transparent illumination is “dead time” or time during a visual inspection during which evaluation of the display panel cannot be performed.
Because of the need to accommodate movement of the transparent illumination unit to perform the reflective illumination inspection, the visual inspector of the related art has a large overall footprint. Moreover, moving the transparent illumination unit to carry out the reflective illumination inspection increases dead time by the time taken to complete the movement of the transparent illumination unit.
When inspecting large sized display panels, the inspection distance must be increased in proportion to the size of the display panel, which may further increase the overall footprint of the visual inspector of the related art.
Limitations in the luminance of the transparent illumination unit of the related art may limit the precision of the transparent illumination inspection, particularly when the inspection distance is large.